Query 'lean' option doesn't produce POJOs

The Query docs state that when using lean “documents returned from queries with the lean option enabled are plain javascript objects, not MongooseDocuments.”. However, the fact that the _id key of the document is an object, not a string contradicts this indicated POJO nature. Surely the _id key should be a string when converting to a plain javascript object.

Currently, checking equality requires a toString call on any _ids, for example when an _id has been supplied by http request and needs to be compared to an _id of a lean query result.

Is there a way to ensure _id is a string, not an object?

const Promise = require('bluebird');
const mongoose = require('mongoose')

mongoose.Promise = Promise;
mongoose.connect('mongodb://localhost/test');

const personSchema = mongoose.Schema({ name : String });

const Person = mongoose.model('Person', personSchema);

const p = new Person({ name : 'Turing' });

return p.save().then(() => {
  Person.findOne({ name : 'Turing' }).then((doc) => {
    console.log('non-lean _id type', typeof doc._id, doc._id)
  });

  Person.findOne({ name : 'Turing' }).lean(true).then((doc) => {
    console.log('    lean _id type', typeof doc._id, doc._id)
  });
});

Produces output:

non-lean _id type object 57c38e4a01456bbc213b7ff2
    lean _id type object 57c38e4a01456bbc213b7ff2

[vkarpov15]

There’s been some discussion about this before, can’t quite remember the issue. The point is that ObjectId is not a mongoose construct, but a fundamental mongodb construct. The point of lean() is to bypass all of mongoose’s heavy change tracking and get the same result that you would get from running the query using the mongodb driver directly. Converting ObjectIds to their hex string representation would break that, so I guess this would require documentation changes more than anything else.

What’s your use case for wanting _id as a string? JSON.stringify() should convert it to a string for you just fine.

[vkarpov15]

Yeah. In my code I always just use toHexString(), this checks the ids for equality and ensures that both are probably mongodb objectids unless you happen to get another object with such a function.